Sleepy Mornings? Time to Go Camping!

Natural daylight resets internal clocks of humans away from artificial light

(RxWiki News) Hit the snooze alarm five times. Drag yourself out of bed. Squint your way into the kitchen to make coffee so you can wake up. Sound familiar? Only in the modern world.

According to a recent study, the sleepiness we feel in the morning after waking up is most likely a result of living in an environment filled with artificial light.

A small experiment with a group of eight adults showed how their natural sleep cycles adjusted to the natural sunlight cycle after just one week of camping.

The hormone telling their brain to sleep "turned off" before they woke up while camping, so their normal sleepiness wasn't there.

"Try matching your sleep schedule to natural light."

This study, led by Kenneth P. Wright, Jr., of the Sleep and Chronobiology Laboratory at the University of Colorado at Boulder, investigated how lack of exposure to artificial light affected sleep patterns.

All humans have internal "clocks" called circadian rhythms. Circadian rhythms are influenced by our exposure to light.

These circadian rhythms determine when we are tired and need to sleep and when we need to wake up.

When artificial light, mostly electric light, became widespread in society, it altered our natural wake-sleep cycles.

But how much it changed us, no one really knows.

To learn how the body adjusts when artificial electric light was not around, the researchers studied eight participants during a two-week experiment during July in the Rocky Mountains.

The eight people, average age 30, included six men and two women who were observed during their normal routines.

These routines included ", school, social activities, self-selected sleep schedules and exposure to the electrical-lighting constructed environment."

Then, the eight participants spent one week camping in tents outdoors with no lights except natural light from the sun or camp fires.

They had no flashlights, no lanterns, no personal electronic devices like cell phones or tablets or any other form of artificial light.

During this trip, they also selected their own sleep schedule, going to sleep when they felt they were tired and waking up when it felt right.

The researchers found that the participants were exposed to more than four times as much light during the camping week than during the normal life week.

Light can be measured in units called lux. The participants were exposed to an average of 979 lux while awake during their week in normal life and an average 4,487 lux while awake during the camping trip.

Humans' internal clocks are most sensitive to light exposure during their first two hours awake in terms of "resetting" their clock for the following day.

So the researchers looked at the participants' light exposure in their first two hours awake in the morning.

In the natural light setting (camping), the participants were exposed to an average 3,074 lux during those two hours.

In their "normal-life" setting with electrical light, they were exposed to an average 934 lux during those two hours.

"The only time of day when participants were exposed to more light during electrical versus natural lighting was between sunset and sleep start time, when the human circadian clock is most sensitive to light-induced phase delays," the authors wrote.

A light-induced phase delay means that a person feels like staying up later rather than going to sleep because of their body's exposure to (artificial) light.

The researchers also found differences in the time of day when the participants' bodies naturally released the hormone melatonin, which tells the body it's time to sleep.

In the artificial lighting environment, the participants' bodies began releasing melatonin about two hours before they fell asleep, which was about 12:30 am. The melatonin "turned off" at about 8 am when they woke up.

In the week of natural lighting, all those times moved up about two hours earlier. Melatonin was released about the time of sunset in the participants and turned off just after sunrise before the participants woke up.

The participants slept about the same number of hours in both scenarios: an average 6.7 hours in artificial lighting and 6.8 hours in natural lighting.

The "efficiency" of their sleep (how well they slept) was also similar: 88 percent efficiency in the artificial light environment and 87 percent in the natural environment.

The study therefore confirmed a basic fact of biology in terms of how humans' internal clocks work: "...internal biological time under natural light-dark conditions tightly synchronizes to environmental time, and in this regard, humans are comparable to other animals," the study authors wrote.

But the study also found evidence to explain why people feel sleepy when they wake up.

Sleepiness lasts up to two hours after a person typically wakes up, which matches up with when the person's melatonin "turns off" in artificial lighting environments.

"That we are most sleepy from a circadian perspective after habitual wake time may be a consequence of the change in the circadian timing of wake time in the electrical-lighting constructed environment," the authors suggested.

"After exposure to natural light, we found the timing of the circadian clock to be about two hours earlier and melatonin offset to occur more than 50 minutes prior to wake time," they wrote.

In other words, if our internal clocks were in harmony with the natural light-dark cycle, the shift in our cycles and when our melatonin offset occurred might make it easier to wake up in the morning.

Meanwhile, the earlier melatonin onset in the evening would "promote earlier bedtimes," instead of the "later bedtimes and disturbed sleep" that artificial light exposure may cause by keeping the brain "awake."

The researchers also found that the participants' clocks became more similar to one another, regardless if each person was more of a "night owl" or "early bird," during the natural light conditions.

"This very interesting study emphasizes the importance of natural, particularly exposure in the morning as far as resetting the biological clock," said William Kohler, MD, a dailyRx expert and the director of the Florida Sleep Institute in Spring Hill, Florida. "This has significant implications for a number of sleep problems, including insomnia."

Dr. Kohler pointed out that many people may not realize the importance of bright light in the morning.

"People may ask why would light in the morning help me get to sleep at night, but it helps reset the biological clock and makes it more likely that we're going to be able to get to sleep at the appropriate time at night," he said. "We need to emphasize that exposure to bright outside light in the morning is very important as far as resetting our biological clock and helping us get a good night's sleep the following night."

The study was published August 1 in the journal Current Biology. The research was funded by the National Institutes of Health. No information on disclosures was reported.

Review Date: 
August 1, 2013